WP_PROXY_PORT - Proxy port for connection. No default, must be defined.

*

WP_PROXY_USERNAME - Proxy username, if it requires authentication.

*

WP_PROXY_PASSWORD - Proxy password, if it requires authentication.

*

WP_PROXY_BYPASS_HOSTS - Will prevent the hosts in this list from going through the proxy.
* You do not need to have localhost and the site host in this list, because they will not be passed
* through the proxy. The list should be presented in a comma separated list, wildcards using * are supported, eg. *.wordpress.org